Atomistic mechanism of carbon nanotube cutting catalyzed by nickel under the electron beam

The cutting of single-walled carbon nanotubes by an 80 keV electron beam catalyzed by nickel clusters is imaged in situ using aberration-corrected high-resolution transmission electron microscopy. Extensive molecular dynamics simulations within the CompuTEM approach provide insight into the mechanism of this process and demonstrate that the combination of irradiation and nickel catalyst is crucial for the cutting process to take place. The atomistic mechanism of cutting is revealed by detailed analysis of irradiation-induced reactions of bonds reorganization and atom ejection in the vicinity of the nickel cluster, showing a highly complex interplay of different chemical transformations catalysed by the metal cluster. One of the most prevalent pathways includes three consecutive stages: formation of polyyne carbon chains from carbon nanotube, dissociation of the carbon chains into single and pairs of adatoms adsorbed on the nickel cluster, and ejection of these adatoms leading to the cutting of nanotube. Significant variations in the atom ejection rate are discovered depending on the process stage and nanotube diameter. The revealed mechanism and kinetic characteristics of cutting process provide fundamental knowledge for the development of new methodologies for control and manipulation of carbon structures at the nanoscale. INTRODUCTION Transitions metals are widely used as catalysts for nanotube growth (see Ref. 1 for review) and graphene formation.2 Recently the processes opposite to growth and formation, i.e. the etching and transformation of carbon nanostructures in the presence of transition metals, have also attracted considerable attention. These processes include metal-assisted etching of graphene3-9